Packet transmission node device realizing packet transfer scheme and control information transfer scheme using multiple virtual connections

ABSTRACT

A packet transmission node which realizes a packet transfer scheme in which a plurality of virtual connections for different qualities of service are set up in correspondence to a multicast destination address, and output virtual connection identifiers are stored in correspondence to destination addresses in a routing table, so that a packet is transferred to output virtual connections determined by referring to the routing table according to a destination address of a packet. A packet transmission node also realizes a control information transfer scheme in which different output virtual connections are set up for a user data packet and a control packet having an identical destination address, and output virtual connection identifiers are stored in correspondence to destination addresses and upper layer protocol identifiers in a routing table, so that a packet is transferred to an output virtual connection determined by referring to the routing table according to a destination address and an upper layer protocol identifier of a packet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a packet transmission node device whichfunctions as a router or a host for transmitting and receiving packetsby being connected to a virtual connection oriented network, and apacket transfer scheme and a control information transfer scheme used ina packet transmission node device.

2. Description of the Background Art

A virtual connection oriented network is a network based on techniquessuch as ATM (Asynchronous Transfer Mode), frame relay, fiber channel,HIPPI (High Performance Parallel Interface), etc.

On such a network, it is possible to realize a multicast in which apacket sent by a sender to a destination address for multicast (amulticast address) in a network layer is distributed to a plurality ofreceivers by the network. In the following, for the sake of simplicity,a case of an IP (Internet Protocol) multicast communication on an ATMnetwork which uses IP as the network layer will be described.

FIG. 1 shows a conventional scheme for transferring a packet destined toa multicast address G in an IP multicast communication system. In FIG.1, H0 to H9 are hosts, where H0 is a sender, and H1, H2, H4, H5, H6, H7and H8 are receivers. R is a router for transferring a packet, which isconnected with the hosts H0 to H9 through ATM connections.

When the network layer is IP, each node (host or router) belongs to alogical group called IP subnet. The communication within the same IPsubnet is realized by the direct transfer without passing through arouter, while the communication between different IP subnets is realizedby utilizing a packet transfer at a router. In FIG. 1, H0, H8 and Rbelong to an IP subnet A, H1, H2, H3 and R belong to an IP subnet B, H4,H5, H6, H7 and R belong to an IP subnet C, and H9 and R belong to an IPsubnet D.

The direct transfer within the same IP subnet can be realized by usingeither a point-to-multipoint ATM connection or a multicast server (MCS)for carrying out a transfer by duplicating a packet.

In such an IP multicast communication system, a conventional procedurefor transferring a packet sent to the multicast address G from a host H0is as follows.

First, the host H0 transfers a packet destined to G to the host H8 andthe router R by using a point-to-multipoint ATM connection. The host H8then receives this packet and processes the received packet suitably,while the router R transfers this packet to the other subnets (subnets Band C) which have hosts participating in this multicast address G.

In the subnet B, the packet is transferred from the router R to themulticast server MCS by using a point-to-point ATM connection, and themulticast server MCS transfers this packet to the hosts H1 and H2 byusing a point-to-multipoint ATM connection. On the other hand, in thesubnet C, the packet is transferred from the router R to the hosts H4,H5, H6 and H7 by using a point-to-multipoint ATM connection. The subnetD has no host which is participating in this multicast address G, sothat the packet is not transferred to the subnet D.

In this manner, a conventional multicast communication scheme uses onepoint-to-multipoint connection or one point-to-point connection to amulticast server in transferring the packet between nodes, so that onlyone and the same quality of service can be provided with respect to onemulticast address, and it has been impossible to realize a multicast inwhich different qualities of service can be provided with respect todifferent receivers participating in one and the same multicast address.

Now, at a time of transferring a packet to a next hop node from a packettransmission node such as a router or a host connected to the virtualconnection oriented network, a virtual connection to that next hop nodeis set up according to a prescribed connection set up protocol, and apacket transfer is carried out by using a set up virtual connection.

The packets exchanged between transmitting and receiving terminal nodesinclude actual data between terminal applications as well as varioustypes of control messages, such as a message for a resource reservationfor the purpose of requesting a desired communication quality.

In a currently available router connected to the virtual connectionoriented network, the identical transfer processing is applied to allthe packets which have the identical destination node address,regardless of whether each packet is carrying the user data or thecontrol message. Namely, in a case of the transfer to the virtualconnection oriented network, a routing table is referred according tothe destination node address of each packet, and then each packet istransmitted to the identical virtual connection according to the routingtable, regardless of whether each packet is carrying the user data orthe control message.

However, when the control information and the actual communicationinformation are transferred through the same virtual connection, thefollowing problems arise.

(1) In a case of adopting the expansion of the router architecture asdescribed in the Internet Draft"draft-katsube-router-atm-overview-00.txt" (which realizes a fastertransfer processing by directly connecting an input virtual connectionand an output virtual connection inside a router, without carrying out anetwork layer processing), it becomes impossible to recognize thecontrol message at a router.

In this case, there is a need to provide a mechanism for extracting onlythose frames (or cells) received from one virtual connection whichcorrespond to the control message packets, and carrying out anappropriate processing to the extracted control message packets, so asto be able to transfer the other user data frames (or cells) withoutcarrying out the packet level processing. However, an incorporation ofsuch a mechanism causes an increase of a cost for the packettransmission node.

(2) When a problem occurs in the virtual connection which istransferring the user data, the transfer of both the user data and thecontrol message will be stopped, so that there is a possibility for acase in which a handling such as a substitute route selection requiredat a time of the problem in the virtual connection cannot be carried outproperly.

(3) It is impossible to control a plurality of related virtualconnections by using a single virtual connection.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a packettransmission node device and a packet transfer scheme capable ofrealizing a multicast in which different qualities of service can beprovided with respect to different receivers participating in one andthe same multicast address.

It is another object of the present invention to provide a packettransmission node device and a control information transfer scheme inwhich it becomes possible to recognize the control message at a routereven when an expanded router architecture is used.

It is another object of the present invention to provide a packettransmission node device and a control information transfer scheme inwhich a handling such as a substitute route selection required at a timeof a problem in the virtual connection can be carried out properly.

It is another object of the present invention to provide a packettransmission node device and a control information transfer scheme inwhich it is possible to control a plurality of related virtualconnections by using a single virtual connection.

According to one aspect of the present invention, there is provided apacket transmission node device, comprising: a routing table for storingoutput virtual connection identifiers in correspondence to destinationaddresses, including identifiers of a plurality of virtual connectionsfor different qualities of service in correspondence to a multicastdestination address; and transfer means for transferring a packet tooutput virtual connections determined by referring to the routing tableaccording to a destination address of said packet.

According to another aspect of the present invention, there is provideda method of packet transmission from a packet transmission node,comprising the steps of: setting up a plurality of virtual connectionsfor different qualities of service in correspondence to a multicastdestination address; storing output virtual connection identifiers incorrespondence to destination addresses, including identifiers of saidplurality of virtual connections for different qualities of service setup in correspondence to the multicast destination address, in a routingtable of the packet transmission node; and transferring a packet fromthe packet transmission node to output virtual connections determined byreferring to the routing table according to a destination address ofsaid packet.

According to another aspect of the present invention there is provided apacket transmission node device, comprising: a routing table for storingoutput virtual connection identifiers in correspondence to destinationaddresses and upper layer protocol identifiers, including identifiers ofdifferent output virtual connections for a user data packet and acontrol packet having an identical destination address; and transfermeans for transferring a packet to an output virtual connectiondetermined by referring to the routing table according to a destinationaddress and an upper layer protocol identifier of said packet.

According to another aspect of the present invention there is provided amethod of packet transmission from a packet transmission node,comprising the steps of: setting up different output virtual connectionsfor a user data packet and a control packet having an identicaldestination address; storing output virtual connection identifiers incorrespondence to destination addresses and upper layer protocolidentifiers, including identifiers of said different output virtualconnections set up for a user data packet and a control packet having anidentical destination address, in a routing table of the packettransmission node; and transferring a packet to an output virtualconnection determined by referring to the routing table according to adestination address and an upper layer protocol identifier of saidpacket.

Other features and advantages of the present invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an IP communication system showing anexemplary overview of packet flow in a conventional IP multicastcommunication scheme.

FIG. 2 is a schematic diagram of an IP communication system showing anexemplary overview of packet flow in a packet transfer scheme accordingto the first embodiment of the present invention.

FIG. 3 is a block diagram of a basic configuration of a packettransmission node device according to the present invention.

FIG. 4 is a diagram showing an exemplary content of a routing table inthe packet transmission node device of FIG. 3 according to the firstembodiment of the present invention.

FIG. 5 is a flow chart for a packet transmission procedure according tothe first embodiment of the present invention.

FIG. 6 is a schematic diagram of an IP communication system showing anexemplary virtual connection setting in a control information transferscheme according to the second embodiment of the present invention.

FIG. 7 is a diagram showing an exemplary content of a routing table inthe packet transmission node device of FIG. 3 corresponding to thevirtual connection setting of FIG. 6 according to the second embodimentof the present invention.

FIG. 8 is a schematic diagram of an IP communication system showing anexemplary virtual connection setting in a control information transferscheme according to the third embodiment of the present invention.

FIG. 9 is a diagram showing an exemplary content of a routing table inthe packet transmission node device of FIG. 3 corresponding to thevirtual connection setting of FIG. 8 according to the third embodimentof the present invention.

FIG. 10 is a schematic diagram of an IP communication system showing anexemplary virtual connection setting in a control information transferscheme according to the fourth embodiment of the present invention.

FIG. 11 is a diagram showing an exemplary content of a routing table inthe packet transmission node device of FIG. 3 corresponding to thevirtual connection setting of FIG. 10 according to the fourth embodimentof the present invention.

FIG. 12 is a schematic diagram of an IP communication system showing anexemplary virtual connection setting in a control information transferscheme according to the fifth embodiment of the present invention.

FIG. 13 is a diagram showing an exemplary content of a routing table inthe packet transmission node device of FIG. 3 corresponding to thevirtual connection setting of FIG. 12 according to the fifth embodimentof the present invention.

FIG. 14 is a schematic diagram of an IP communication system showing anexemplary virtual connection setting in a control information transferscheme according to the sixth embodiment of the present invention.

FIG. 15 is a diagram showing an exemplary content of a routing table inthe packet transmission node device of FIG. 3 corresponding to thevirtual connection setting of FIG. 14 according to the sixth embodimentof the present invention.

FIG. 16 is a schematic diagram of an IP communication system showing anexemplary overview of packet flow in a case where the packet transferscheme and the control information transfer scheme according to thepresent invention are combined together.

FIG. 17 is a diagram showing an exemplary content of a routing table inthe packet transmission node device of FIG. 3 corresponding to thevirtual connection setting of FIG. 16 for a case of combining the packettransfer scheme and the control information transfer scheme according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 2 to FIG. 5, the first embodiment of a packettransmission node device for realizing a packet transfer schemeaccording to the present invention will be described in detail.

In short, in this first embodiment, a node device connected with atleast one virtual connection oriented network has a memory means forstoring information including a source address, a destination address,an output interface, an output virtual connection identifier, and aquality of service. This node device also has a transfer means fortransferring a packet by referring to the memory means according to adestination address or a pair of a source address and a destinationaddress of a transmitting packet, determining an output interface and anoutput virtual connection, and controlling a packet transmission meansof the determined output interface to transmit the packet through thedetermined output virtual connection.

The memory means stores a plurality of output virtual connectionidentifiers in correspondence to a plurality of qualities of servicewith respect to a destination group address or a pair of a sourceaddress and a destination group address, so that a plurality ofpoint-to-multipoint connections are used with respect to one groupaddress. Consequently, it becomes possible to provide differentqualities of service with respect to different output virtualconnections, i.e., with respect to different receivers participating inthis group address.

In addition, the above described mechanism of the node device of thisfirst embodiment can be used along with the conventional multicastdelivery mechanism, such that the conventional mechanism can be utilizedwhen all the hosts participating in the same multicast address arerequesting the identical quality of service, while the mechanism of thisfirst embodiment can be utilized when there are hosts which requestdifferent qualities of service.

Now, the multicast packet transfer scheme at the node device (a host ora router) in this first embodiment will be described in further detail.In the following, the overview of the packet flow in this multicastpacket transfer scheme will be described first, and then the node deviceconfiguration and the packet transmission procedure in this firstembodiment will be described.

FIG. 2 shows an exemplary overview of the packet flow in this multicastpacket transfer scheme. In FIG. 2, H0 to H9 are hosts, where H0 is asender, R0 and R1 are routers for transferring packets, and H1, H2, H4,H5, H6, H7 and H8 are receivers which correspond to the group address G.The router R0 is connected with the hosts H0 to H9 except for H7 and therouter R1 through ATM connections, and #1, #2 and #3 depicted around therouter R0 indicate output interface numbers of this router R0.

When the network layer is IP, each node (host or router) belongs to alogical group called IP subnet. The communication within the same IPsubnet is realized by the direct transfer without passing through arouter, while the communication between different IP subnets is realizedby utilizing a packet forwarding at a router. In FIG. 2, H0, H8 and R0belong to an IP subnet A, H1, H2, H3 and R0 belong to an IP subnet B,R0, H4, H5, H6 and R1 belong to an IP subnet C, and H9 and R0 belong toan IP subnet D. The IP subnet B has a multicast server (MCS) forcarrying out a transfer by duplicating a packet.

In FIG. 2, a procedure for transferring a packet sent to the multicastaddress G from a host H0 is as follows.

First, the host H0 transfers a packet destined to G to the host H8 andthe router R0 by using a point-to-multipoint ATM connection. The host H8then receives this packet and processes the received packet suitably,while the router R0 transfers this packet to the other subnets (subnetsB and C) which have hosts participating in this multicast group G.

In the subnet B, the packet is transferred from the router R0 to themulticast server MCS though the output interface #2 by using apoint-to-point ATM connection with the identifier VPI/VCI=10/105 at theoutput interface corresponding to QOS=1, and the multicast server MCStransfers this packet to the hosts H1 and H2 by using apoint-to-multipoint ATM connection.

On the other hand, in the subnet C, the packet is transferred from therouter R0 to the hosts H4 to H6 and the router R1 through the outputinterface #3 by using two point-to-multipoint ATM connections with theidentifiers VPI/VCI=10/100 and VPI/VCI=10/101 at the output interfacecorresponding to QOS=1 and QOS=2, respectively, as indicated in FIG. 2.

The subnet D has no host which is participating in this multicast groupG, so that the packet is not transferred to the subnet D.

In order to transfer the packet of the identical destination to two ATMconnections by duplicating the packet at the router in the abovedescribed manner, the router R0 carries out the following packettransmission procedure. Note that FIG. 2 shows an exemplary case inwhich this packet transfer is carried out by the router R0, but thesimilar packet transfer can also be carried out by a host fortransmitting a packet, so that the packet transmission procedure will bedescribed below for a node in general, which can be either a router or ahost.

First, FIG. 3 shows a node device configuration in this firstembodiment, where solid lines indicate the packet flow, while a dashedline indicates the control information flow related to a tablereferring. In this configuration of FIG. 3, a node device 100 comprisesa packet reception unit 101, a packet analysis and transfer unit 102connected with the packet reception unit 100, a packet transmission unit103 connected with the packet analysis and transfer unit 102, upperlayers 104 connected with the packet analysis and transfer unit 102, anda routing table 105 which is referred to by the packet analysis andtransfer unit 102.

The packet reception unit 101 is connected with a LAN (Local AreaNetwork) such as ATM, and functions to assemble a network layer packetfrom datalink layer frames received from the LAN according to a protocolof the LAN. Here, the datalink layer frames are given by ATM cells, andthe network layer packet is given by an IP packet.

The packet analysis and transfer unit 102 judges whether a packetreceived at the packet reception unit 101 is a packet destined to thisnode 100 or not. When the received packet is destined to this node 100,this packet will be given to the upper layers 104, whereas when thereceived packet is not destined to this node 100, the packet analysisand transfer unit 102 carries out the network layer processing, refersto the packet header, and determines an output interface and a next hopnode or an output connection identifier according to the routing table105. In a case of ATM, the output connection is a VC (Virtual Channel)and the output connection identifier is VPI/VCI. The packet analysis andtransfer unit 102 also handles a packet given from the upper layers 104similarly by carrying out the network layer processing, and determiningan output interface and a next hop node or an output connectionidentifier according to the routing table 105.

The packet transmission unit 103 converts the packet given from thepacket analysis and transfer unit 102 into the datalink layer frames ofthe connected LAN, and transmits the converted datalink layer frames tothe LAN according to the next hop node or the output connectionidentifier given by the packet analysis and transfer unit 102.

The upper layers 104 are protocols above the network layer such as TCP(Transmission Control Protocol), or UDP (User Datagram Protocol). Morespecifically, the upper layers 104 can be a routing protocol forexchanging routing information, an application software, an RSVP(Resource Reservation Protocol) message, etc.

The routing table 105 is a table to be referred by the packet analysisand transfer unit 102. This routing table 105 is set up eitherstatically in advance, or dynamically by the routing protocol.

For an exemplary case shown in FIG. 2, this routing table 105 has acontent as shown in FIG. 4. In this routing table of FIG. 4, the outputVPI/VCI and the quality of service (QOS) can be searched out by usingthe source address and the destination address of the packet to betransferred as a search key. It is also possible to use the destinationaddress alone as a search key, without using the transmission source.

When the packet is assigned with an importance level according to ascheme such as a hierarchical coding to be described below such thatwhich packet is to be transmitted is determined according to thisimportance level, the multicast packet is transferred or transmitted byreferring to the quality of service in the routing table, but when thepacket is not assigned with an importance level or when all the packetsare to be transmitted, there is no need to refer to the quality ofservice in the routing table at a time of actually transferring ortransmitting the multicast packet.

In this first embodiment, there is a possibility for transmitting onepacket to a plurality of interfaces and a plurality of output virtualconnections, so that it is necessary for the routing table 105 to have aplurality of output I/Fs and a plurality of output VPI/VCIs with respectto a single destination address or a single pair of the source addressand the destination address. For this reason, the routing table shown inFIG. 4 is formed by a linked list in which a plurality of output routesare linked by pointers.

In FIG. 4, the routing table has such a setting that, when the source H0receives a packet with the destination address G, this packet will betransferred to an ATM connection (A) with the output I/F=#3, the outputVPI/VCI=10/100, and QOS=1; an ATM connection (B) with the output I/F=#3,the output VPI/VCI=10/101, and QOS=2; and an ATM connection (C) with theoutput I/F=#2, the output VPI/VCI=10/105, and QOS=1.

Here, for the node group of H1, H2, H4, H5, H6, and R1 corresponding tothe multicast group G, the ATM connection (A) is a point-to-multipointconnection terminated at the hosts H4 and H5, the ATM connection (B) isa point-to-multipoint connection terminated at the host H6 and therouter R1, and the ATM connection (C) is a point-to-point connection tothe multicast server MCS, which is connected with thepoint-to-multipoint connection from the multicast server MCS to thehosts H1 and H2.

Note that it is possible to make various modifications to this setting,such as a modification to change the above described ATM connection (A)into a point-to-point connection to a multicast server for makingconnection with the point-to-multipoint connection to the hosts H4 andH5, for example.

When the receivers (H4, H5, H6, and R1, for example) request therespective qualities of service (a bandwidth requested by H4 and H5 islarger than a bandwidth requested by H6 and R1, for example), thesetting of the ATM connections and the routing table is made by settingup the ATM connections (a VC of QOS=1 terminated at H4 and H5, and a VCof QOS=2 terminated at H6 and R1) to satisfy the requested qualities ofservice, and registering information on these connections in the routingtable 105.

The packet transmission procedure in this first embodiment is carriedout according to the flow chart of FIG. 5 as follows. This procedure isto be carried out when a router receives the multicast packet at thepacket reception unit 101 and transfers this packet to the next hopnode, or when a host transmits a packet from the upper layers 104.

The packet given to the packet analysis and transfer unit 102 isanalyzed, and the routing table 105 is searched by using the source andthe destination address of that packet (step S1). Here, it is alsopossible to carry out the search by using the destination address alone.As long as the output route is registered in the routing table 105, theregistered output route is referred and the packet is transmitted to theregistered output I/F and output VPI/VCI according to the quality ofservice specified for each connection (step S2). Here, the packettransmission according to the quality of service implies the packettransmission while dropping packets according to the quality of service.For example, an importance level assigned to each packet can beregistered within each packet according to the hierarchical codingscheme, such that the packets to be transmitted can be selectedaccording to this importance level and the quality of service specifiedfor each connection.

This processing is repeated as many times as necessary, and when theprocessing to transmit one packet is completed for all the outputconnections registered in the routing table 105, this packettransmission procedure is terminated. In this manner, it is possible totransfer the packet of the identical destination to a plurality of ATMconnections by duplicating the packet.

In an exemplary case shown in FIG. 2, when the packet with the sourceaddress H0 and the destination address G is received at the router R0,the routing table 105 is searched, and this packet is transferred to theATM connection (A) with the output I/F=#3, the output VPI/VCI=10/100,and the QOS=1 first. Then, by searching the routing table 105 further,this packet is also transferred to the ATM connection (B) with theoutput I/F=#3, the output VPI/VCI=10/101, and the QOS=2. Finally, bysearching the routing table 105 further, this packet is also transferredto the ATM connection (C) with the output I/F=#2, the outputVPI/VCI=10/105, and the QOS=1, so as to complete the packet transfer.

As described, according to this first embodiment, a plurality of outputvirtual connections including point-to-multipoint connections are madeavailable with respect to one multicast address, so that it becomespossible to provide different qualities of service with respect todifferent output virtual connections, i.e., with respect to differentreceivers participating in this multicast group.

Referring now to FIG. 6 to FIG. 15, the second to sixth embodiments of apacket transmission node device for realizing a control informationtransfer scheme according to the present invention will be described indetail.

In the following, it is to be understood that a virtual connectionoriented network is a network based on techniques such as ATM(Asynchronous Transfer Mode), frame relay, fiber channel, HIPPI (HighPerformance Parallel Interface), etc.

It is also to be understood that a packet transmission node is either apacket switching device such as a router or a packettransmission/reception terminal.

It is also to be understood that a node address is given by an IPaddress, a MAC address, an address of IPX, an address of AppleTalk, etc.

It is also to be understood that a control packet is a packet used for aresource reservation protocol such as STII (Stream Protocol II) and RSVP(Resource Reservation Protocol), which is to be exchanged betweentransmission and reception terminals through a packet transmission node,for example.

In short, in the control information transfer scheme according to thepresent invention, when a packet transmission node transmits a packet toa next hop node by using a virtual connection, the virtual connection towhich the packet is to be transmitted is determined by referring therouting table according to both a destination node address field and aprotocol identifier in the packet header at the packet analysis andtransfer unit. Namely, the routing table is formed such that an outputinterface and an output virtual connection can be obtained by using boththe destination address field and the protocol identifier as a searchkey. Here, it is also possible to use a source address as a search keyin addition.

In one aspect of the control information transfer scheme according tothe present invention, two types of virtual connections for controlpackets and for user data packets are separately provided, even forthose control packets and user data packets which have the samedestination node address (unicast or multicast) and which are to betransferred (transmitted) to the same next hop node (the same next hopnode group in a case of multicast). Then the control packets and theuser packets are transferred (transmitted) by using the respectivevirtual connections according to the setting in the routing table.

In another aspect of the control information transfer scheme accordingto the present invention, among those packets which have the samedestination group address, the user data packets are transferred(transmitted) by using a virtual connection for transferring(transmitting) to a next hop node group which should receive/transferthe packets having the above noted group address. On the other hand, forthe control packets, a virtual connection for transferring(transmitting) the control packets altogether to a packet transmissionnode group including a next hop node group which should receive/transferthe packets having the above noted group address as well as a next hopnode group which should receive/transfer the packets having other groupaddress different from the above noted group address. Then, the controlpackets are transferred (transmitted) altogether by using that virtualconnection.

Now, with references to FIG. 6 and FIG. 7, the second embodiment of apacket transmission node device for realizing a control informationtransfer scheme according to the present invention will be described indetail.

In this second embodiment, the configuration of the packet transmissionnode device is basically the same as that of FIG. 3 in the firstembodiment described above.

In a case where the packet transmission node device 100 is a router,when a packet is received from the packet reception unit 101, a networklayer packet (an IP datagram in a case of IP) is assembled from thedatalink layer frames (cells in a case of ATM), and given to the packetanalysis and transfer unit 102.

At the packet analysis and transfer unit 102, an output interface and anoutput virtual connection for transmitting this packet are determined bysearching the routing table 105 according to the header information ofthe received packet, and this packet is sent to the packet transmissionunit 103 corresponding to the determined output interface.

At the packet transmission unit 103, this packet is converted into thedatalink layer frames (cells in a case of ATM), and the converteddatalink layer frames are transmitted to the output virtual connectiondetermined by the packet analysis and transfer unit 102.

Now, with references to FIG. 6 and FIG. 7, the control informationtransfer scheme in this second embodiment will be described for anexemplary case in which the packet transmission node device is a router.

FIG. 6 shows an exemplary network system configuration in this secondembodiment. In FIG. 6, routers R1, R2 and R3 are connected to a virtualconnection oriented network N, and the other routers R and hosts Hconnected with these routers R1, R2 and R3 are connected toconnection-less networks such as Ethernets.

In this exemplary configuration, the content of the routing table at therouter R1 is as shown in FIG. 7, which is to be referred in a case oftransferring packets which have destination addresses "a.b.c.d","p.q.x.y" and "e.f.g.h" of the hosts.

The search key to be used in searching this routing table of FIG. 7 isthe destination IP address and the protocol identifier in the packetheader. The protocol identifier indicates whether the upper layerprotocol of that packet is TCP or UDP (which also indicates that it is auser data packet), or if it is a control message for RSVP, etc. (whichalso indicates that it is a control packet). As a result of searchingthis routing table, the information such as the output interfaceindicating an interface port to which the packet should be outputted,the next hop node address indicating an IP address of the next hop node,and the identifier of the virtual connection to which the packet shouldbe outputted (an identifier VPI/VCI of a VC (Virtual Channel) of an ATMconnection is used in FIG. 7 as an example) can be obtained.

In a case of searching by using the destination IP address alone as asearch key as in a case of a conventional routing table, the packets aregoing to be outputted to the same virtual connection regardless ofwhether the upper layer protocol is TCP or UDP, or whether it is acontrol message for RSVP, etc. or not. In contrast, in this secondembodiment, as shown in FIG. 7, the packets are outputted to differentvirtual connections when the upper layer protocols are different evenwhen the destination IP address is the same.

Namely, for the packet with the destination IP address "a.b.c.d", the IPaddress of the next hop router is "p.q.r.s", and as the virtualconnection up to that next hop router, the virtual connection withVPI/VCI=100/200 is provided for data transfer (user data packettransfer), while the virtual connection with VPI/VCI=100/201 is providedfor RSVP control message (path message) transfer (control packettransfer).

Also, for the packet with the destination IP address "p.q.x.y", the IPaddress of the next hop router is "p.q.r.s", and as the virtualconnection up to that next hop router, the virtual connection withVPI/VCI=100/100 is provided for data transfer, while the virtualconnection with VPI/VCI=100/201 is also used for RSVP control messagetransfer. In this manner, the control packets having differentdestination IP addresses and the same next hop node can be transferredby using the same virtual connection.

Also, for the packet with the destination IP address "e.f.g.h", the IPaddress of the next hop router is "p.q.r.t", and as the virtualconnection up to that next hop router, the virtual connection withVPI/VCI=500/888 is provided for data transfer, while the virtualconnection with VPI/VCI=500/777 is provided for RSVP control messagetransfer.

Here, the set up of each virtual connection can be realized by the ATMsignaling procedure or the management procedure.

Next, with references to FIG. 8 and FIG. 9, the third embodiment of apacket transmission node device for realizing a control informationtransfer scheme according to the present invention will be described indetail.

In this third embodiment, the configuration of the packet transmissionnode device is basically the same as that of FIG. 3 in the firstembodiment described above.

FIG. 8 shows an exemplary network system configuration in this thirdembodiment. In FIG. 8, routers R1, R2, R3 and R4 are connected to avirtual connection oriented network N. This third embodiment is directedto a case of the multicast communication using the IP group address.

In this exemplary configuration, the content of the routing table at therouter R1 is as shown in FIG. 9, which is to be referred in a case oftransferring packets which have the group addresses "225.0.0.100" and"230.10.10.0" as the destination addresses.

The search key to be used in searching this routing table of FIG. 9 isthe destination group address (multicast address) and the protocolidentifier in the packet header (and possibly the source address). As aresult of searching this routing table, the information such as theoutput interface Indicating an interface port to which the packet shouldbe output, and the identifier of the virtual connection to which thepacket should be output (an identifier VPI/VCI of a VC (Virtual Channel)of an ATM connection is used in FIG. 9 as an example) can be obtained.

FIG. 8 shows an exemplary case in which the routers R2 and R3 areparticipating in the group address "225.0.0.100", while the routers R3and R4 are participating in the group address "230.10.10.0". In otherwords, the hosts participating in the group address "225.0.0.100" existon a downstream side of the routers R2 and R3, while the hostsparticipating in the group address "230.10.10.0" exist on a downstreamside of the routers R3 and R4.

In this third embodiment, as shown in FIG. 9, the packets are output todifferent virtual connections when the upper layer protocols aredifferent even when the destination group address is the same.

Namely, for the packet with the destination group address "225.0.0.100",the point-to-multipoint virtual connection with VPI/VCI=50/100 connectedto R2 and R3 is provided for data transfer, while thepoint-to-multipoint virtual connection with VPI/VCI=50/200 connected toR2 and R3 is provided for RSVP control message transfer.

Also, for the packet with the destination group address "230.10.10.0",the point-to-multipoint virtual connection with VPI/VCI=100/10 connectedto R3 and R4 is provided for data transfer, while thepoint-to-multipoint virtual connection with VPI/VCI=100/11 connected toR3 and R4 is provided for RSVP control message transfer.

Here, the set up of each virtual connection is going to be realized bythe ATM signaling procedure or the management procedure.

Next, with references to FIG. 10 and FIG. 11, the fourth embodiment of apacket transmission node device for realizing a control informationtransfer scheme according to the present invention will be described indetail.

In this fourth embodiment, the configuration of the packet transmissionnode device is basically the same as that of FIG. 3 in the firstembodiment described above.

FIG. 10 shows an exemplary network system configuration in this fourthembodiment. In FIG. 10, the third embodiment of FIG. 8 is modified byincorporating a multicast server (MCS) in order to provide the multicastcommunications of a plurality of senders efficiently.

In this fourth embodiment, the manner of utilizing virtual connectionsfor data transfer is the same as in the third embodiment describedabove. On the other hand, as a virtual connection for RSVP controlmessage transfer to the destination group address "225.0.0.100", avirtual connection with VPI/VCI=25/888 connected to the MCS is utilized,and the MCS which received the control message through this virtualconnection then transfers the control messages to the routers R2 and R3on the downstream side by using a point-to-multipoint virtual connectionwith VPI/VCI=20/444 connected to the routers R2 and R3.

In this case, it is not necessary for every transmission node to have apoint-to-multipoint virtual connection for control message transfer tothe multicast address "225.0.0.100", and it suffices for eachtransmission node to have a point-to-point virtual connection to theMCS, so that it is possible to expect a reduction of a number of virtualconnections compared with a case of having as many point-to-multipointvirtual connections as a number of senders as in the third embodimentdescribed above.

In this exemplary configuration, the content of the routing table at therouter R1 is as shown in FIG. 11.

In this fourth embodiment, as shown in FIG. 11, the packets are outputto different virtual connections when the upper layer protocols aredifferent even when the destination group address is the same.

Namely, for the packet with the destination group address "225.0.0.100",the point-to-multipoint virtual connection with VPI/VCI=50/100 connectedto R2 and R3 is used for data transfer when the upper layer protocol isTCP (user data packet), while the point-to-point virtual connection withVPI/VCI=25/888 connected to the MCS is used for RSVP control messagetransfer when the upper layer protocol is RSVP (control packet). Thisvirtual connection with VPI/VCI=25/888 is a point-to-point virtualconnection from which packets are forwarded by the MCS to apoint-to-multipoint virtual connection with VPI/VCI=20/444 connected toR2 and R3.

Here, the set up of each virtual connection is going to be realized bythe ATM signaling procedure or the management procedure.

Note that the MCS can determine the output interface and the outputvirtual connection according to VPI/VCI of the received cell. In a caseof the configuration of FIG. 10, the MCS has such a setting that thepoint-to-multipoint virtual connection with VPI/VCI=20/444 is determinedaccording to VPI/VCI of the received cell. Here, in order to avoid theinterleaving at the cell level in a case where the control messages froma plurality of senders (which are received through different virtualconnections) are to be transmitted to the same point-to-multipointvirtual connection, it is preferable to assemble the cell up to the AAL(ATM Adaptation Layer) frame. Alternatively, it is also possible toassemble a packet from the received cell at the MCS, and determine theoutput VPI/VCI by referring to the destination group address as in ausual router.

Note also that the above described fourth embodiment is directed to anexemplary case in which only the control packets are transferred byusing the MCS, but it is also possible to transfer the user data packetsby using the MCS as well. In such a case, however, the virtualconnection for data transfer and the virtual connection for controlmessage transfer are to be provided separately in accordance with thepresent invention.

Next, with references to FIG. 12 and FIG. 13, the fifth embodiment of apacket transmission node device for realizing a control informationtransfer scheme according to the present invention will be described indetail.

In this fifth embodiment, the configuration of the packet transmissionnode device is basically the same as that of FIG. 3 in the firstembodiment described above.

FIG. 12 shows an exemplary network system configuration in this fifthembodiment. In this fifth embodiment, the manner of utilizing virtualconnections for data transfer is the same as in the third embodimentdescribed above. On the other hand, as a virtual connection for RSVPcontrol message transfer, a virtual connection with VPI/VCI=50/333connected to all of R2, R3 and R4 is utilized. This virtual connectionis provided in correspondence to an IP address "224.0.0.1" which meansall local nodes participating in the multicast communication.

In this exemplary configuration, the content of the routing table at therouter R1 is as shown in FIG. 13.

The search key to be used in searching this routing table of FIG. 13 isthe destination group address (multicast address) and the protocolidentifier in the packet header (and possibly the source address).

In this fifth embodiment, as shown in FIG. 13, the packets are output todifferent virtual connections when the upper layer protocols aredifferent even when the destination group address is the same.

Namely, for the packet with the destination group address "225.0.0.100",the point-to-multipoint virtual connection with VPI/VCI=50/100 connectedto R2 and R3 is used for data transfer when the upper layer protocol isTCP (user data packet), while the point-to-multipoint virtual connectionwith VPI/VCI=50/333 connected to all of R2, R3 and R4 is used for RSVPcontrol message transfer when the upper layer protocol is RSVP (controlpacket).

Also, for the packet with the destination group address "230.10.10.0",the point-to-multipoint virtual connection with VPI/VCI=100/10 connectedto R3 and R4 is used for data transfer, while the point-to-multipointvirtual connection with VPI/VCI=50/333 is also used for RSVP controlmessage transfer.

In addition, the packets with the destination group address "224.0.0.1"are also transferred by the point-to-multipoint virtual connection withVPI/VCI=50/333. This IP address "224.0.0.1" is used for the packetcommunication in which the upper layer protocol is IGMP (Internet GroupManagement Protocol) for example.

The virtual connection with VPI/VCI=50/333 is a point-to-multipointvirtual connection destined to R2, R3 and R4 which is set up withrespect to the IP address "224.0.0.1".

Here, the set up of each virtual connection is going to be realized bythe ATM signaling procedure or the management procedure.

In this fifth embodiment, all the multicast participating nodes aremembers of the address "224.0.0.1" so that when the control messages aretransmitted to the point-to-multipoint virtual connection destined tothis address "224.0.0.1", each downstream side node is going to receivethe messages not relevant to that node, but it suffices to discard suchmessages not relevant to each node at the receiving side.

Note that the above described fifth embodiment is directed to anexemplary case in which the control packets are transmitted to thevirtual connection which is set up to be destined to all the local nodesparticipating in the multicast communication, but using theconfiguration similar to that of FIG. 12, it is also possible to specifysome multicast groups among a plurality of existing multicast groups,and transmit the control packets to a point-to-multipoint virtualconnection which is set up to be destined to the local nodesparticipating in any of the specified multicast groups (nodes for whichthe hosts participating in the specified multicast group exist on theirdownstream sides).

Next, with references to FIG. 14 and FIG. 15, the sixth embodiment of apacket transmission node device for realizing a control informationtransfer scheme according to the present invention will be described indetail.

In this sixth embodiment, the configuration of the packet transmissionnode device is basically the same as that of FIG. 3 in the firstembodiment described above.

FIG. 14 shows an exemplary network system configuration in this sixthembodiment. In FIG. 14, the fifth embodiment of FIG. 12 is modified byincorporating a multicast server (MCS) in order to provide the multicastcommunications of a plurality of senders efficiently.

In this sixth embodiment, the manner of utilizing virtual connectionsfor data transfer is the same as in the fifth embodiment describedabove. On the other hand, as a virtual connection for RSVP controlmessage transfer to the destination group address "224.0.0.1" describedabove, a virtual connection with VPI/VCI=25/888 connected to the MCS isutilized, and the MCS which received the control message through thisvirtual connection then transfers the control messages to the routersR2, R3 and R4 on the downstream side by using a point-to-multipointvirtual connection with VPI/VCI=10/555 connected to the routers R2, R3and R4 and destined to the address "224.0.0.1".

In this case, it is not necessary for every transmission node to have apoint-to-multipoint virtual connection for control message transfer tothe multicast address "224.0.0.1", and it suffices for each transmissionnode to have a point-to-point virtual connection to the MCS, so that itis possible to expect a reduction of a number of virtual connectionscompared with a case of having as many point-to-multipoint virtualconnections as a number of senders as in the fifth embodiment describedabove.

In this exemplary configuration, the content of the routing table at therouter R1 is as shown in FIG. 15.

In this sixth embodiment, as shown in FIG. 15, the packets are output todifferent virtual connections when the upper layer protocols aredifferent even when the destination group address is the same.

Namely, for the packet with the destination group address "225.0.0.100",the point-to-multipoint virtual connection with VPI/VCI=50/100 connectedto R2 and R3 is used for data transfer when the upper layer protocol isTCP (user data packet), while the point-to-point virtual connection withVPI/VCI=25/888 connected to the MCS is used for RSVP control messagetransfer when the upper layer protocol is RSVP (control packet).

Also, for the packet with the destination group address "230.10.10.0",the point-to-multipoint virtual connection with VPI/VCI=100/10 connectedto R3 and R4 is used for data transfer, while the point-to-point virtualconnection with VPI/VCI=25/888 is also used for RSVP control messagetransfer.

In addition, the packets with the destination group address "224.0.0.1"are also transferred by the point-to-point virtual connection withVPI/VCI=25/888.

The virtual connection with VPI/VCI=25/888 is a point-to-point virtualconnection from which packets are forwarded by the MCS to apoint-to-multipoint virtual connection with VPI/VCI=10/555 connected toR2, R3 and R4.

Here, the set up of each virtual connection is going to be realized bythe ATM signaling procedure or the management procedure.

Note that the MCS can determine the output interface and the outputvirtual connection according to VPI/VCI of the received cell. In a caseof the configuration of FIG. 14, the MCS has such a setting that thepoint-to-multipoint virtual connection with VPI/VCI=10/555 is determinedaccording to VPI/VCI of the received cell. Here, in order to avoid theinterleaving at the cell level in a case where the control messages froma plurality of senders (which are received through different virtualconnections) are to be transmitted to the same point-to-multipointvirtual connection, it is preferable to assemble the cell up to the AAL(ATM Adaptation Layer) frame. Alternatively, it is also possible toassemble a packet from the received cell at the MCS, and determine theoutput VPI/VCI by referring to the destination group address as in ausual router.

Note also that this sixth embodiment is directed to an exemplary case inwhich only the control packets are transferred by using the MCS, but itis also possible to transfer the user data packets by using the MCS aswell. In such a case, however, the virtual connection for data transferand the virtual connection for control message transfer are to beprovided separately in accordance with the present invention.

As described, according to the second to sixth embodiments, it becomespossible to separate the virtual connection to be used for the user datapacket transmission and the virtual connection to be used for thecontrol packet transmission, by using the information other than thedestination address in determining the output virtual connection foreach packet.

Consequently, when this control information transfer scheme is appliedto a router within which the input virtual connection and the outputvirtual connection are directly connected, it becomes possible torecognize and handle the control message at the router by concatenatingthe input and output virtual connections used for the user data packettransmission, while carrying out the network layer processing for thevirtual connection to be used for the control message packettransmission.

Also, even when a problem occurs in the virtual connection which istransferring the user data packets, it is still possible to transfer thecontrol packets.

In addition, it becomes possible to control a plurality of relatedvirtual connections simultaneously, by means of a single virtualconnection.

Thus, according to the control information transfer scheme of thepresent invention, it becomes possible to recognize the control messageat a router even when an expanded router architecture is used, ahandling such as a substitute route selection required at a time oftrouble in the virtual connection can be carried out properly, and it ispossible to control a plurality of related virtual connections by usinga single virtual connection.

It is to be noted that the packet transfer scheme of the firstembodiment described above and the control information transfer schemeof any of the second to sixth embodiment described above can be realizedsimultaneously by the same packet transmission node device.

For instance, as shown in FIG. 16, the packet transfer scheme of FIG. 2described above may be modified by incorporating an additional virtualconnection with VPI/VCI=10/444 connected to the hosts H4 to H6 and therouter R1, which is to be used for control message packet transferaccording to the control information transfer scheme of the presentinvention.

In this case, the routing table of the packet transmission node devicehas a content as shown in FIG. 17, which effectively combines a contentsimilar to that of FIG. 4 for user data packet transfer and a contentsimilar to that of FIGS. 7, 9, 11, 13 or 15 for control packet transfer.

It is also to be noted that, besides those already mentioned above, manymodifications and variations of the above embodiments may be madewithout departing from the novel and advantageous features of thepresent invention. Accordingly, all such modifications and variationsare intended to be included within the scope of the appended claims.

What is claimed is:
 1. A packet transmission node device, comprising:arouting table for storing output virtual connection identifiers incorrespondence to destination addresses, including identifiers of aplurality of virtual connections for different qualities of service incorrespondence to a multicast destination address; and transfer meansfor transferring a packet to output virtual connections determined byreferring to the routing table according to a destination address ofsaid packet.
 2. The device of claim 1, wherein the routing table storeseach output virtual connection identifier in correspondence to a pair ofa source address and a destination address, and the transfer meansrefers to the routing table according to a source address and adestination address of said packet.
 3. The device of claim 1, whereinthe routing table also stores an output interface of the devicecorresponding to each output virtual connection identifier.
 4. Thedevice of claim 1, wherein the routing table also stores a quality ofservice corresponding to each output virtual connection identifier. 5.The device of claim 1, wherein a packet destined to the multicastdestination address is to be transmitted to a node group correspondingto a multicast group including a plurality of sub-node groups, and therouting table stores the identifiers of said plurality of virtualconnections for different qualities of service which are connected tosaid plurality of sub-node groups.
 6. A method of packet transmissionfrom a packet transmission node, comprising the steps of:setting up aplurality of virtual connections for different qualities of service incorrespondence to a multicast destination address; storing outputvirtual connection identifiers in correspondence to destinationaddresses, including identifiers of said plurality of virtualconnections for different qualities of service set up in correspondenceto the multicast destination address, in a routing table of the packettransmission node; and transferring a packet from the packettransmission node to output virtual connections determined by referringto the routing table according to a destination address of said packet.7. The method of claim 6, wherein the storing step stores each outputvirtual connection identifier in correspondence to a pair of a sourceaddress and a destination address, and the transferring step refers tothe routing table according to a source address and a destinationaddress of said packet.
 8. The method of claim 6, wherein the storingstep also stores an output interface of the packet transmission nodecorresponding to each output virtual connection identifier.
 9. Themethod of claim 6, wherein the storing step also stores a quality ofservice corresponding to each output virtual connection identifier. 10.The method of claim 6, wherein a packet destined to the multicastdestination address is to be transmitted to a node group correspondingto a multicast group including a plurality of sub-node groups, and thestoring step stores the identifiers of said plurality of virtualconnections for different qualities of service which are connected tosaid plurality of sub-node groups.
 11. A packet transmission nodedevice, comprising:a routing table for storing output virtual connectionidentifiers in correspondence to destination addresses and upper layerprotocol identifiers, including identifiers of different output virtualconnections for a user data packet and a control packet having anidentical destination address; and transfer means for transferring apacket to an output virtual connection determined by referring to therouting table according to a destination address and an upper layerprotocol identifier of said packet.
 12. The device of claim 11, whereinthe routing table also stores an output interface of the devicecorresponding to each output virtual connection identifier.
 13. Thedevice of claim 11, wherein the routing table also stores a next hopnode address corresponding to each output virtual connection identifier.14. The device of claim 11, wherein the routing table stores one outputvirtual connection identifier for control packets destined to anidentical next hop node.
 15. The device of claim 11, wherein the routingtable stores an output virtual connection identifier of a point-to-pointvirtual connection connected to a multicast server for a control packetdestined to a multicast destination address, and the multicast servertransmits packets from said point-to-point virtual connection to apoint-to-multipoint virtual connection connected to next hop nodes forsaid control packet.
 16. The device of claim 11, wherein the routingtable stores an output virtual connection identifier of apoint-to-multipoint virtual connection for a plurality of controlpackets destined to different multicast destination addresses, saidpoint-to-multipoint virtual connection being connected to next hop nodesfor said plurality of control packets.
 17. The device of claim 11,wherein the routing table stores one output virtual connectionidentifier for control packets destined to next hop node groupscorresponding to a plurality of multicast groups, while storing oneoutput virtual connection identifier for user data packets destined to anext hop node group corresponding to each multicast group.
 18. Thedevice of claim 11, wherein the routing table stores the output virtualconnection identifiers for user data packets including identifiers of aplurality of virtual connections for different qualities of service incorrespondence to a multicast destination address, and the transfermeans transfers a user data packet destined to the multicast destinationaddress to output virtual connections determined by referring to therouting table according to a destination address and an upper layerprotocol identifier of the user data packet.
 19. The device of claim 18,wherein the routing table stores each output virtual connectionidentifier for user data packets in correspondence to a source addressand a destination address, and the transfer means refers to the routingtable according to a source address and a destination address of theuser data packet.
 20. The device of claim 18, wherein the routing tablealso stores an output interface of the device corresponding to eachoutput virtual connection identifier for user data packets.
 21. Thedevice of claim 18, wherein the routing table also stores a quality ofservice corresponding to each output virtual connection identifier foruser data packets.
 22. The device of claim 18, wherein the user datapacket destined to the multicast destination address is to betransmitted to a node group corresponding to a multicast group includinga plurality of sub-node groups, and the routing table stores theidentifiers of said plurality of virtual connections for differentqualities of service which are connected to one sub-node group.
 23. Amethod of packet transmission from a packet transmission node,comprising the steps of:setting up different output virtual connectionsfor a user data packet and a control packet having an identicaldestination address; storing output virtual connection identifiers incorrespondence to destination addresses and upper layer protocolidentifiers, including identifiers of said different output virtualconnections set up for a user data packet and a control packet having anidentical destination address, in a routing table of the packettransmission node; and transferring a packet to an output virtualconnection determined by referring to the routing table according to adestination address and an upper layer protocol identifier of saidpacket.
 24. The method of claim 23, wherein the storing step also storesan output interface of the packet transmission node corresponding toeach output virtual connection identifier.
 25. The method of claim 23,wherein the storing step also stores a next hop node addresscorresponding to each output virtual connection identifier.
 26. Themethod of claim 23, wherein the storing step stores one output virtualconnection identifier for control packets destined to an identical nexthop node.
 27. The method of claim 23, wherein the storing step stores anoutput virtual connection identifier of a point-to-point virtualconnection connected to a multicast server for a control packet destinedto a multicast destination address, and the multicast server transmitspackets from said point-to-point virtual connection to apoint-to-multipoint virtual connection connected to next hop nodes forsaid control packet.
 28. The method of claim 23, wherein the storingstep stores an output virtual connection identifier of apoint-to-multipoint virtual connection for a plurality of controlpackets destined to different multicast destination addresses, saidpoint-to-multipoint virtual connection being connected to next hop nodesfor said plurality of control packets.
 29. The method of claim 23,wherein the storing step stores one output virtual connection identifierfor control packets destined to next hop node groups corresponding to aplurality of multicast groups, while storing one output virtualconnection identifier for user data packets destined to a next hop nodegroup corresponding to each multicast group.
 30. The method of claim 23,wherein the storing step stores the output virtual connectionidentifiers for user data packets including identifiers of a pluralityof virtual connections for different qualities of service incorrespondence to a multicast destination address, and the transferringstep transfers a user data packet destined to the multicast destinationaddress to output virtual connections determined by referring to therouting table according to a destination address and an upper layerprotocol identifier of the user data packet.
 31. The method of claim 30,wherein the storing step stores each output virtual connectionidentifier for user data packets in correspondence to a source addressand a destination address, and the transferring step refers to therouting table according to a source address and a destination address ofthe user data packet.
 32. The method of claim 30, wherein the storingstep also stores an output interface of the method corresponding to eachoutput virtual connection identifier for user data packets.
 33. Themethod of claim 30, wherein the storing step also stores a quality ofservice corresponding to each output virtual connection identifier foruser data packets.
 34. The method of claim 30, wherein the user datapacket destined to the multicast destination address is to betransmitted to a node group corresponding to a multicast group includinga plurality of sub-node groups, and the storing step stores theidentifiers of said plurality of virtual connections for differentqualities of service which are connected to one sub-node group.